This invention relates to a combine harvester, and more particularly to a combine harvester having control means to automatically shift a traveling change speed mechanism in response to sampled load variations occurring on an engine in order to maintain workloads within a predetermined range.
It is known in the art that this type of combine harvester is constructed so as to travel at controlled speeds according to load variations in order to maintain the workloads within a predetermined range. However, according to the prior art construction, such controls are effected to shift the change speed mechanism immediately in response to sampled results of the load variations, which has the following disadvantages:
Although ordinary operations are relatively free from great load variations, it is often the case to constantly load variations occurring at random which are due to changes in conditions of a field where the operations are conducted, vibrations of the harvester body and the like. Controls involving constant change speed operations in response to such temporary load variations must operate an actuator with great frequency to a disadvantage of shortened life thereof.
It is conceivable to average values of load variations sampled by a predetermined cycle time, to avoid responses to temporary load variations or load variations occurring at randon. However, a control mode for effecting speed changes on the basis of the average of detected load variation values is incapable of effectively coping with abrupt load variations though it is adequate to cope with gentle load variations.
It is impossible to promptly follow such abrupt load variations because of a small amount of change speed operation or a slow action which is based on the averaged amount of load variations.
On the other hand, the known combine harvester as described above which is the type to control the workload by changing its traveling speed has another problem, as follows:
Whether the traveling speed is controlled automatically or manually is determined by the driver in advance, and necessary control parameters are obtained after the automatic control mode is selected. Therefore, a change to the automatic control mode is not effected smoothly when a load condition at a time of hand-operated driving during an idle time greatly differs from an optimal load condition for a working implement by the automatic control. In other words, a sudden acceleration or deceleration may occur inadvertently, which is dangerous, when starting the automatic control, since a control parameter remains undetected then.
In one type of conventional combine harvester, the traveling speed is automatically controlled by operating only an auxiliary change speed mechanism when reaping grain-carrying stalks lying down on the ground, whereas the traveling speed is controlled by operating a main change speed mechanism according to workloads when reaping upstanding stalks. When at this time data indicating low speed traveling is input into a control system, it is impossible to determine whether the input data is due to the operation of the auxiliary change speed mechanism or to an actual increase in the workload. In other words, correct controls cannot be effected on the traveling speed when reaping upstanding stalks rather than lying stalks.
In addition, when insensitivity zones are provided adjacent a control target value, controls outwardly of the insensitivity zones tend to be unsatisfactory, contrary to what one would expect.
Further, it has been an inevitable drawback of the conventional combine harvester that a sudden change in the load which takes place at a start or end of the reaping operation disturbs the traveling speed controls.